Information as to the volume of the left ventricle of the heart as a function of time is useful to a cardiologist in evaluating the heart. In particular, the volume at diastole, the volume at systole, the rate of change of volume and other parameters based on volume provide useful information to the cardiologist.
One approach to determining the volume of the left ventricle of the heart is by ultrasound imaging. The volume is determined from a two-dimensional ultrasound image by determining the cross-sectional area from the ultrasound image and making certain assumptions regarding the shape of the left ventricle.
In one approach, a user selects a still frame apical 4 chamber or apical 2 chamber ultrasound image and manually traces the outline of the ventricle as it appears on the image using a trackball or similar device. In addition, the user selects a long axis which serves as an axis of rotation. The volume is determined by rotating the two-dimensional traced area about the selected axis to provide a circularly symmetric volume. The volume is computed using a technique known as method of disks. After the user has precisely traced the border between the ventricle and the endocardium, the traced region is segmented into a number of parallel slices. The volume of each of the slices is computed. The volumes are summed to provide the volume of the entire ventricle. The segmentation is based on the traced region. In order to determine the volume in another frame, the user precisely traces the ventricle and the volume is calculated in the same way. The segmentation is based on the traced area, which varies from frame to frame. This technique provides the volume one frame at a time and is typically performed only at diastole and systole.
Another technique for determining the volume of a ventricle is described in application Ser. No. 07/614,780, filed Nov. 9, 1990, assigned to the assignee of the present application. Signals from an ultrasound scanner are processed to determine whether they represent blood or tissue. Incremental areas of the image which represent blood and which fall within a region of interest having a truncated annular shape are rotated about the long axis of the ventricle to form an incremental volume of revolution. The total volume of the ventricle is derived by summing the incremental volumes.
In another prior art system, a region of interest is traced by a user on an ultrasound image. Signals from the ultrasound scanner are processed to determine whether they represent blood or tissue. Blood areas within the region of interest are summed in an accumulator to determine the total blood area within the region of interest. The volume is not determined.
All of the prior art techniques for determining ventricular volume have had various disadvantages, including inability to determine volume in real time, excess complexity and the like.